The present invention relates to a method of preserving wood and a composition useful in that method.
The use of various compositions for the treatment and preservation of wood is well-known. For example, U.S. Pat. No. 4,622,248 describes the use of various metal compounds, acids, petroleum byproducts, fungicides and insecticides in wood preservative compositions. Wood preservative compositions containing complexes of copper and amines, and optional additives, are well known. For example, EP 0 864 406 A2 describes such a composition which comprises a moldicide. A popular class of wood preservative compositions are referred to as alkaline copper quat, or ACQ, solutions. The industrial standard for ACQ solutions is published by the American Wood Preservers' Association under standard P5-04 (Standard for Waterborne Preservatives).
Wood that is treated with copper-amine preservatives is susceptible to discoloration caused by fungus and mold. Retailers will not accept such discolored wood. Thus, wood treaters need to ensure that mold and fungus formation is prevented. That is why moldicides, such as 5-chloro-2-methyl-4-isothiazolin-3-one, are popular additives to copper-amine preservative solutions.
Unfortunately, popular isothiazolinone-based moldicides are unstable in ACQ solutions due to their alkalinity. Lowering the pH of the solution to improve the stability of isothiazolinone moldicides causes copper salts to precipitate, rendering the solution unsuitable for use. It would be desirable to have a copper-amine preservative for wood that would support such moldicides yet not suffer from copper salt precipitation.